2017 Volume 123 Issue 9 Pages 707-716
This study concerns the thermodynamics of trace element partitioning and its application to the P-T estimations of metamorphic rocks. Firstly, the application of Henry's law and Raoult's law, which are commonly used for the infinite dilute solutions to analyse trace element partitioning in geothermometry, is discussed. Secondly, P-T estimates based on trace element partitioning, including Zr-in-rutile, Ti-in-zircon and Ti-in-quartz geothermometers, are critically reviewed from practical and thermodynamical viewpoints. In particular, the Ti-in-quartz geothermometer is discussed in detail from the following perspectives: (1) the validity of using ppm amounts for Ti solubility of quartz; (2) the applicability of Nernst's distribution law to Ti partitioning between quartz and rutile containing high levels of impurities; (3) stable phase assemblages derived from the relation between the Gibbs' free energy and the bulk composition in the SiO2-TiO2 system; (4) variations in Ti content in quartz with temperature, as predicted from the SiO2-TiO2 phase diagram; and: (5) activity of the TiO2 component in quartz containing other impurities.
